Fast adaptive power control adapter for a variable multirate communication system

ABSTRACT

A system and a method of controlling transmitter power in a wireless communication system in which user data is processed as a multirate signal having a rate N(t) and in which the user data signal having rate N(t) is converted into a transmission data signal having a faster rate M(t) for transmission. The transmission power is adjusted on a relatively slow basis based on quality of data received by a receiver of the transmitted data. The transmitter power is determined as a function of N(t)/M(t) such that a change in the data rate in the multiple channels or the rate of the transmission data signal is compensated in advance of a quality of data based adjustment associated with such data rate change. Preferably, the user data signal having rate N(t) is converted into the transmission data signal having the faster rate M(t) by repeating selected data bits whereby the energy per bit to noise spectrum density ratio is increased in the transmission data signal.

This application claims priority from U.S. Provisional PatentApplication No. 60/221,348, filed Jul. 26, 2000, and from U.S.Provisional Patent Application No. 60/223,375, filed Aug. 7, 2000.

The present invention relates to power control for wirelesscommunication systems and, in particular, fast adaptive power controlsystem and methods for a variable multirate communication system.

BACKGROUND

Various methods of power control for wireless communication systems arewell known in the art. An example of an open loop power controltransmitter system for a single rate data system is illustrated in FIG.1. An example of a closed loop power control transmitter system for asingle rate data is illustrated in FIG. 2.

The purpose of both systems is to rapidly vary transmitter power in thepresence of a fading propagation channel and time-varying interferenceto minimize transmitter power while insuring that data is received atthe remote end with acceptable quality. Typically, in a digitalimplementation, transmitter power is varied by applying a varying scalefactor to the digital data, as opposed, for example, to varying the gainof an RF amplifier.

In state-of-the-art communication systems such as Third GenerationPartnership Project (3GPP) Time Division Duplex (TDD) and FrequencyDivision Duplex (FDD) systems multiple channels of variable rate dataare combined for transmission. FIGS. 3 and 4 represent prior art openand closed power control transmission systems, respectively. Backgroundspecification data for such systems are found at 3GPP TS 25.223 v3.3.0,3GPP TS 25.222 v3.2.0, 3GPP TS 25.224 v3.6 and Volume 3 specificationsof Air-Interface for 3G Multiple System Version 1.0, Revision 1.0 by theAssociation of Radio Industries Businesses (ARIB).

Such open and closed loop power control systems for variable multiratewireless communications systems respond relatively slowly to data ratechanges, resulting in sub-optimal performance such as relating toexcessive transmitter power and below-quality received signals. It wouldbe desirable to provide a fast method and system of power controladaption for data rate changes resulting in more optimal performance.

SUMMARY

The invention provides a method of controlling transmitter power in awireless communication system in which user data is processed as amultirate signal having a rate N(t) and in which the user data signalhaving rate N(t) is converted into a transmission data signal having afaster rate M(t) for transmission. The transmitter power is controlledby a closed loop system where the transmission power is adjusted byapplying a scale factor in response to step up/down data generated by areceiver of the transmitted data, the step up/down data being based inpart on relatively slowly collected quality of data. The step up/downdata is determined as a function of N(t)/M(t) such that a change in theuser data signal rate or the data rate of the transmission data signalis compensated for in advance of a quality of data based adjustmentassociated with such a data rate change. Preferably, the user datasignal having rate N(t) is converted into the transmission data signalhaving a faster rate M(t) by repeating selected data bits whereby theenergy per bit to noise spectrum density ratio is increased in thetransmission data signal.

In a preferred embodiment, the step up/down data is generated by thereceiver by combining measured interference power data of the signalreceived from the transmitter with target signal to interference ratio(SIR) data which is computed by multiplying nominal target SIR data,based on relatively slowly collected received signal quality data, by afactor N(t)/M(t) so that the target SIR data is quickly adjusted when achange in data rate occurs. Additionally, the transmitter computes thescale factor based on the received step up/down data and √{square rootover ( )}(N(t)/M(t)).

The invention also provides a closed loop transmission power controlsystem for a wireless communication system in which user data isprocessed as a multirate signal having a rate N(t) and in which the userdata signal having rate N(t) is converted into a transmission datasignal having a faster rate M(t) for transmission and in which thetransmission power is adjusted by applying a scale factor in response tostep up/down data. The system includes a receiver which receives theM(t) rate transmission data signal and generates the step up/down data.The receiver preferably has a data signal rate converter which decreasesthe data rate of received transmission data M(t) to produce a user datasignal having a lower rate N(t), a data quality measuring device formeasuring the quality of data of the user data signal, and circuitry forcomputing step up/down data based in part on the measured quality ofdata of the user data signal. The data signal rate converter isassociated with the circuitry to provide rate data such that saidcircuitry computes step up/down data as a function of N(t)/M(t) suchthat a change in the user data signal rate or the rate of thetransmission data signal is compensated for in advance of a quality ofdata based adjustment associated with such data rate change.

The system also preferably includes a transmitter having a data signalrate convertor which converts the user data signal having rate N(t) intothe transmission data signal having a faster rate M(t) by repeatingselected data bits whereby the energy per bit to noise spectrum densityratio is increased in the transmission data signal.

In a preferred embodiment, the receiver has an interference measuringdevice for measuring the power of an interference signal received withthe M(t) rate transmission data signal. The data quality measuringdevice outputs a nominal target SIR data based on relatively slowlycollected received data quality data. The receiver circuitry computesthe step up/down data by combining measured interference power data ofthe signal received from the transmitter with target signal tointerference ratio SIR data which is computed by multiplying the nominaltarget SIR data by a factor N(t)/M(t) so that the target SIR data isquickly adjusted when a change in data rate occurs.

Additionally, in the preferred embodiment, the transmitter includes aprocessor which computes the scale factor based on the step up/down dataand √{square root over ( )}(N(t)/M(t)).

Other objects and advantages will be apparent to those of ordinary skillin the art based upon the following description of presently preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a schematic diagram of a conventional open loop power controlsystem for single rate data wireless communication.

FIG. 2 is a schematic diagram of a conventional closed loop powercontrol system for single rate data wireless communication.

FIG. 3 is a schematic diagram of a conventional open loop power controlsystem for variable multirate data wireless communication.

FIG. 4 is a schematic diagram of a conventional closed loop powercontrol system for variable multirate data wireless communication.

FIG. 5 is a block diagram of data rate up-conversion from 6 to 8 bitsper block using repetition.

FIG. 6 is a block diagram of data rate down-conversion of repeated datafrom 8 to 6 bits per block.

FIG. 7 is a schematic diagram of a fast adaptive open loop power controlsystem for variable multirate data wireless communication made inaccordance with the teaching of the present invention.

FIG. 8 is a schematic diagram of a fast adaptive closed loop powercontrol system for variable multirate data wireless communication madein accordance with the teaching of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Conventional power control methods for wireless systems such as 3G PPutilize so-called inner and outer loops. The power control system isreferred to as either open or closed dependent upon whether the innerloop is open or closed. The outer loops of both types of systems areclosed loops.

Pertinent portions of an open loop power control system having a“transmitting” communication station 10 and a “receiving” communicationstation 30 are shown in FIG. 1. Both stations 10, 30 are transceivers.Typically one is a base station and the other a type of user equipment(UE). For clarity, only selected components are illustrated.

The open loop power control transmitting station 10 includes atransmitter 11 having a data line 12 which transports a user data signalfor transmission. The user data signal is provided with a desired powerlevel which is adjusted by applying a transmit power scale factor froman output 13 of a processor 15 to adjust the transmission power level.The user data is transmitted from an antenna system 14 of thetransmitter 11.

A wireless radio signal 20 containing the transmitted data is receivedby the receiving station 30 via a receiving antenna system 31. Thereceiving antenna system will also receive interfering radio signals 21which impact on the quality of the received data. The receiving station30 includes an interference power measuring device 32 to which thereceived signal is input which device 32 outputs measured interferencepower data. The receiving station 30 also includes a data qualitymeasuring device 34 into which the received signal is also input andwhich device 34 produces a data quality signal. The data qualitymeasuring device 34 is coupled with a processing device 36 whichreceives the signal quality data and computes target signal tointerference ratio (SIR) data based upon a user defined quality standardparameter received through an input 37.

The receiving station 30 also includes a transmitter 38 which is coupledwith the interference power measuring device 32 and the target SIRgenerating processor 36. The receiving station's transmitter 38 alsoincludes inputs 40, 41, 42 for user data, a reference signal, andreference signal transmit power data, respectively. The receivingstation 30 transmits its user data and the control related data andreferences signal via an associated antenna system 39.

The transmitting station 10 includes a receiver 16 and an associatedreceiving antenna system 17. The transmitting station's receiver 16receives the radio signal transmitted from the receiving station 30which includes the receiving station's user data 44 and the controlsignal and data 45 generated by the receiving station 30.

The transmitting station processor 15 is associated with thetransmitting station's receiver 16 in order to compute the transmitpower scale factor. The transmitter 11 also includes a device 18 formeasuring received reference signal power which device 18 is associatedwith path loss computing circuitry 19.

In order to compute the transmit power scale factor, the processor 15receives data from a target SIR data input 22 which carries the targetSIR data generated by the receiver station's target SIR generatingprocessor 36, an interference power data input 23 which carries theinterference data generated by the receiving station's interferencepower measuring device 32, and a path loss data input 24 which carries apath loss signal that is the output of the path loss computing circuitry19. The path loss signal is generated by the path loss computingcircuitry 19 from data received via a reference signal transmit powerdata input 25 which carries the reference signal transmit power dataoriginating from the receiving station 30 and a measured referencesignal power input 26 which carries the output of the reference signalpower measuring device 18 of the transmitter 11. The reference signalmeasuring device 18 is coupled with the transmitting station's receiver16 to measure the power of the reference signal as received from thereceiving station's transmitter 38. The path loss computing circuitry 19preferably determines the path loss based upon the difference betweenthe known reference power signal strength conveyed by input 25 and themeasured received power strength conveyed by input 26.

Interference power data, reference signal power data and target SIRvalues are signaled to the transmitting station 10 at a ratesignificantly lower than the time-varying rate of the propagationchannel and interference. The “inner” loop is the portion of the systemwhich relies on the measured interface. The system is considered “openloop” because there is no feedback to the algorithm at a rate comparableto the time-varying rate of the propagation channel and interferenceindicating how good the estimates of minimum required transmitter powerare.

With respect to the outer loop of the open loop power control system ofFIG. 1, at the remote receiver station 30, the quality of the receiveddata is evaluated via the measuring device 34. Typical metrics fordigital data quality are bit error rate and block error rate.Computation of these metrics requires data accumulated over periods oftime significantly longer than the period of the time-varyingpropagation channel and interference. For any given metric, there existsa theoretical relationship between the metric and received SIR. Whenenough data have been accumulated in the remote receiver to evaluate themetric, it is computed and compared with the desired metric(representing a desired quality of service) in processor 36 and anupdated target SIR is then output. The updated target SIR is that value(in theory) which applied in the transmitter inner loop would cause themeasured metric to converge to the desired value. Finally, the updatedtarget SIR is passed, via the receiving station transmitter 38 and thetransmitting station receiver 16, to the transmitter 11 via input 22 foruse in its inner loop. The update rate of target SIR is bounded by thetime required to accumulate the quality statistic and practical limitson the signaling rate to the power-controlled transmitter 11.

With reference to FIG. 2, a communication system having a transmittingstation 50 and a receiving station 70 which employs a closed loop powercontrol system is illustrated.

The transmitting station 50 includes a transmitter 51 having a data line52 which transports a user data signal for transmission. The user datasignal is provided with a desired power level which is adjusted byapplying a transmit power scale factor from an output 53 of a processor55 to adjust the power level. The user data is transmitted via anantenna system 54 of the transmitter 51.

A wireless radio signal 60 containing the transmitted data is receivedby the receiving station 70 via a receiving antenna system 71. Thereceiving antenna system will also receive interfering radio signals 71which impact on the quality of the received data. The receiving station70 includes a measuring device 72 to which the received signal is inputwhich device 72 outputs measured SIR data. The receiving station 70 alsoincludes a data quality measuring device 73 into which the receivedsignal is also input and which device 73 produces a data quality signal.The data quality measuring device 73 is coupled with a processor 74which receives the signal quality data and computes target signal tointerference ratio (SIR) data based upon a user defined quality standardparameter received through an input 75.

A combiner 76, preferably a subtracter, compares the measured SIR datafrom the device 72 with the computed target SIR data from the processor74, preferably by subtracting, to output an SIR error signal. The SIRerror signal from the combiner 76 is input to processing circuitry 77which generates step up/down commands based thereon.

The receiving station 70 also includes a transmitter 78 which is coupledwith the processing circuitry 77. The receiving station's transmitter 78also includes an input 80 for user data. The receiving station 70transmits its user data and the control related data via an associateantenna system 79.

The transmitting station 50 includes a receiver 56 and an associatedreceiving antenna system 57. The transmitting station's receiver 56receives the radio signal transmitted from the receiving station 70which includes the receiving station's user data 84 and the control data85 generated by the receiving station.

The transmitting station's scale factor processor 55 has an input 58associated with the transmitting station's receiver 56. The processor 55receives the up/down command signal through input 58 and computes thetransmit power scale factor based thereon.

With respect to the inner loop of the closed loop power control system,the transmitting station's transmitter 51 sets its power based uponhigh-rate “step-up” and “step-down” commands generated by the remotereceiving station 70. At the remote receiving station 70, the SIR of thereceived data is measured by the measuring device 72 and compared viacombiner 76 with a target SIR value generated by the processor 74. Thetarget SIR is that value (in theory) which, given that the data isreceived with that value, results in a desired quality of service. Ifthe measured received SIR is less than the target SIR, a “step-down”command is issued by the processing circuitry 77, via the receivingstation's transmitter 78 and the transmitting station's receiver 56, tothe transmitter 51, otherwise a “step-up” command is issued. The powercontrol system is considered “closed-loop” because of the high-ratefeedback of the “step-up” and “step-down” commands which react in realtime to the time-varying propagation channel and interference. Ifrequired transmit power level changes due to time varying interferenceand propagation, it quickly responds and adjusts transmit poweraccordingly.

With respect to the outer loop of the closed loop power control system,the quality of the received data is evaluated in the receiving station70 by the measuring device 73. Typical metrics for digital data qualityare bit error rate and block error rate. Computation of these metricsrequires data accumulated over periods of time significantly longer thanthe period of the time-varying propagation channel and interference. Forany given metric, there exists a theoretical relationship between themetric and received SIR. When enough data has been accumulated in theremote receiver to evaluate the metric, it is computed and compared withthe desired metric (representing a desired quality of service) by theprocessor 74 and an updated target SIR is then output. The updatedtarget SIR is that value (in theory) which applied in the receiveralgorithm would cause the measured metric to converge to the desiredvalue. The updated target SIR is then used in the inner loop todetermine the direction of the step up/down commands sent to thetransmitting station's power scale generating processor 55 to controlthe power of the transmitter 51.

FIGS. 1 and 2 illustrate power control systems for single rate datatransmissions. However, in a digital communications system, data can beprocessed in blocks with a given bit rate and given block size, oralternatively, a given number of bits per block and given block rate. Insuch systems, for example, 3GPP FDD and TDD systems, more than one datarate can exist at any given time within the communications system, andsuch data rates can vary over time. FIG. 3 illustrates a modifiedopen-loop power control system and FIG. 4 illustrates a modifiedclosed-loop power control system for wireless systems which communicatemultiple data channels having variable data rates.

To accommodate variable rate data transmission, the open loop powercontrol system illustrated in FIG. 1 is modified, as shown in FIG. 3, toinclude an up converter 27 in the transmitting station 10 and a downconverter 47 in the receiving station 30.

The user data for transmission is a signal, or for multichannel iscombined into a signal, having a data rate N(t). The data stream havingthe rate N(t) is converted to a data stream having a higher rate M(t) bydata up converter 27 which has an output 28 which carries thetransmission data signal having the rate M(t).

At the receiving station 30, the user data signal having the rate M(t)is received and down converted by the converter 47 to the original rateN(t). The interference power measuring device 32 measures theinterference of the signal as received with its higher M(t) rate. Thedata quality measuring device 34 is coupled to the user data pathdownstream from the converter 47 and measures the quality of the dataafter it has been down converted to the N(t) rate.

To accommodate variable rate data transmission, the closed loop powercontrol system illustrated in FIG. 2 is modified, as shown in FIG. 4, toinclude an up converter 67 in the transmitting station 50 and a downconverter 87 in the receiving station 70. The user data for transmissionis a signal, or for multichannel is combined into a signal, having adata rate N(t). The data stream having the rate N(t) is converted to adata stream having a higher rate M(t) by data up converter 67 which hasan output 68 which carries the transmission data signal having the rateM(t).

At the receiving station 70, the user data signal having the rate M(t)is received and down converted by the converter 87 to the original rateN(t). The interference power measuring device 72 measures theinterference of the signal as received with its higher M(t) rate. Thedata quality measuring device 73 is coupled to the user data streamdownstream from the converter 87 and measures the quality of the dataafter it has been down converted to the N(t) rate.

In both types of variable rate systems, the user data input to thetransmitter 11, 51 for transmission to the remote receiver 30, 70 hasthe data rate denoted N(t) and the user data output from the remotereceiver is at that same rate. Data rate N(t) can be the composite ofseveral data rates of different data channels which have beenmultiplexed for transmission over a common bearer. That N is a functionof time (t) indicates that the rate may vary, that is, be different fromtime to time, or from block to block. Reasons for this variation includethe addition and/or deletion of data channels and actual data ratechanges in existing channels, as is typical for packet services.

Also in both systems, illustrated in FIGS. 3 and 4, in the transmit datapath, the date rate is changed from N(t) to M(t) and change back to N(t)in the remote receiver. Data rate N(t) is the user data rate and thedata rate M(t) is over-the-air data rate, which can be independent ofeach other.

In a 3GPP TDD system, for example, M(t) is the number of bits per 10msec. frame in a given number of time slots and orthogonal variablespreading factor codes at given spreading factors. That M is a functionof time (t) indicates that the rate may vary, that is, be different fromtime to time, or more specifically, from frame-to-frame. Varying M isequivalent to varying the spreading factors and/or number of physicalchannels used per frame, varying N is equivalent to a data rate changein one or more transport channels. Rate M(t) is equivalent to N_(dataj)bits per 10 msec. frame and N(t) is equivalent to${{PL} \cdot {1/{RM}_{\min}}}{\sum\limits_{TrCHi}\quad {{RM}_{i} \cdot N_{ij}}}$

bits per 10 msec. frame, during the time t when TFCj is in effect,where, as defined in 3GPP:

N_(ij) is the number of bits in a radio frame before rate matching onTrCH i with transport format combination j.

RM_(i) is the semi-static rate matching attribute for TrCH i which issignaled from higher layers.

RM_(min) is the minimum semi-static rate matching attribute for TrCHswithin the coded composite TrCH.

PL is the puncturing limit which value limits the amount of puncturingthat can be applied in order to minimize the number of physical channelsand is signaled from higher layers.

N_(dataj) is the total number of bits that are available for a codedcomposite TrCH in a radio frame with transport format combination j.

TF_(i)(j) is the transport format of TrCH i for the transport formatcombination j.

TB or Transport Block is defined as the basic data unit exchangedbetween Layer 1 and MAC. An equivalent term for Transport Block is “MACPDU”.

TBS or Transport Block Set is defined as a set of Transport Blocks thatis exchanged between Layer 1 and MAC at the same time instance using thesame Transport Channel.

TrCH or Transport Channel are the channels offered by the physical layerto Layer 2 for data transport between peer Layer 1 entities are denoted.Different types of Transport Channels are defined by how and with whichcharacteristics data is transferred on the physical layer, e.g. whetherusing dedicated or common physical channels.

TF or Transport Format is defined as a format offered by Layer 1 to MACfor the delivery of a Transport Block Set during a Transmission TimeInterval on a Transport Channel. The Transport Format constitutes of twoparts—one dynamic part and one semi-static part.

TFC or Transport Format Combination is defined as the combination ofcurrently valid Transport Formats on all Transport Channels, i.e.containing one Transport Format from each Transport Channel.

TFCS or Transport Format Combination Set is defined as a set ofTransport Format Combinations.

MAC or Medium Access Control is a sub-layer of radio interface Layer 2providing unacknowledged data transfer service on logical channels andaccess to Transport Channels.

PDU or Protocol Data Unit is a unit of data specified in an (N)-protocollayer and consisting of (N)-protocol control information and possibly(N)-user data.

The conversion from rate N(t) to rate M(t) is performed in thetransmitting station 10, 50 in the converter 27,67 which indicatesup-conversion by the factor M(t)/N(t). The conversion rate from rateM(t) back to rate N(t) is performed in the remote receiving station 30,70 in the converter 47, 87 which indicates down-conversion by the factorN(t)/M(t).

In both systems illustrated in FIGS. 3 and 4, rate M(t) is shown to behigher than rate N(t). This is deliberate. An unintended effect of theupward rate conversion, mitigation of which is an object of theinvention, occurs only for case of up-conversion by repetition in thetransmitter, which is described below. This effect does not happen ifN(t)=M(t) and the effect is different if N(t)>M(t) which is not thesubject of this invention.

Up-conversion of a data rate can be implemented by repetition, that is,repeating selected bits in a rate −N block until it contains the samenumber of bits as a block at rate M and to perform down-conversion bynumerically combining the received repeated “soft” bits. Up-conversionby repetition is illustrated in an example shown in FIG. 5, where B_(i)is the i^(th) “hard” bit, that is ±1, in the input sequence, for thesimplified case of increasing the data rate from six to eight bits perblock. In the example, two bits, 2 and 5, are repeated, changing theblock size from six to eight. In FIG. 6, where b_(i)+n_(j) is a “soft”bit, that is, a digital sample within the receiver of the transmittedbit B_(i) plus noise component n_(j) at time j, the down-conversionprocess, with input consisting of eight “soft” bits is illustrated.Received “soft” bits 2 and 3 are numerically summed to form a scaledversion of the original bits 2 and 3; similarly, received “soft” bits 6and 7 are numerically summed to form a scaled version of the originalbit 5.

The particular repeated bits used in the example represent uniformdistribution of repeated bits, which, in conjunction with aninterleaver, is a particular scheme used in a 3GPP system. However, thechoice of bits to repeat is not germane to the invention.

The above-described method of data rate conversion is a component ofso-called “rate matching” using repetition functions used in the 3GPPTDD and FDD systems. It has the advantage, over the simplistic method ofsending (two, in the example) dummy bits to change the data rate, inthat the energy difference between the original shorter and transmittedlonger block can be exploited to improve signal quality. To illustrate,in the example, received bits 2 and 5 have twice the energy per bitnoise spectrum density ratio (Eb/No) of the other received bits. Thisresults in an overall improvement of bit error and block error rates ofthe received data as compared to what those quality metrics would havebeen had the bits not been repeated and two dummy bits been sentinstead. Of course, eight units of energy were used to transmit dataonly requiring six units of energy. There are as a result the effect ofthe unintended but consequential increased transmission energy and theeffect of improved received data quality. Those effects are addressed bythe present invention.

The open and closed power control systems shown in FIGS. 3 and 4 forvariable multirate data are virtually the same as those shown in FIGS. 1and 2 for single rate data. FIG. 3 and FIG. 4 represent open and closedpower control systems for a 3GPP TDD communication system. However, boththe open and closed loop power control systems are less than optimal inaddressing the effects of rate changes for variable multirate data.

In the open loop system of FIG. 3, with N(t) equal to M(t) in the steadystate and ignoring the variance of a fading channel or any variableinterference, the target SIR will settle at a quiescent point yieldingthe desired data quality. This condition is equivalent to the singlerate example of FIG. 1. In a variable rate system, however, at some timet, N, and/or M changes. As described above, where this results in animprovement to the measured data quality metric, more energy than isactually required is transmitted. The outer loop, which operates at arelatively low rate, will eventually detect the improved signal qualityand then lower the target SIR for the inner loop to reduce transmitterpower to compensate for what it perceives as too-high signal quality. Inthe meantime, the transmitter 11 will be using more energy than isactually necessary to transmit the data (to have it received with therequired quality). In the case of an open loop power controlled transmitstation being a battery powered mobile unit (as can be the case in a3GPP system), unnecessary battery power is expended.

The invention as it applies to open loop power control for variablemultirate data is illustrated in FIG. 7 where corresponding elements areidentified with the same reference numbers as in FIG. 3. As shown inFIG. 7, the transmitting station's converter 27 provides an additionalinput 29 to the scale factor generating processor 15. Though input 29,the converter provides a signal equivalent to √{square root over ()}(N(t)/M(t)) to the processor 15 as a factor in calculating thetransmit power scale factor. Accordingly, when the modified scale factoris applied to the transmitted data, it causes the transmit power to beadjusted by the factor of:

N(t)/M(t)

to immediately compensate for the rate change in N(t) or M(t).

This modified scale factor is applied in the same manner as is theconventional scale factor that sets transmitter power, which is derivedfrom:

P _(TS) =SIR _(TARGET) +I _(RS)+α(L−L ₀)+L ₀+CONSTANT VALUE  Equation 1

where the additive terms represent multiplicative factors expressed indB. As a practical matter, the additional factor used in generating thescale factor becomes simply another term in the above equation, which inthe above form becomes:

P _(TS) =SIR _(TARGET) +I _(RS)+α(L−L ₀)+L ₀+CONSTANTVALUE+N(t)/M(t)  Equation 2

where:

P_(TS) is the transmitting station's transmission power level indecibels.

SIR_(TARGET) is determined in the receiving station.

I_(RS) is the measure of the interference power level at the receivingstation.

L is the path loss estimate in decibels for the most recent time slotfor which the path loss was estimated.

L₀, the long term average of the path loss in decibels, is the runningaverage of the pathloss estimate, L.

CONSTANT VALUE is a correction term. The CONSTANT VALUE corrects fordifferences in the uplink and downlink channels, such as to compensatefor differences in uplink and downlink gain. Additionally, the CONSTANTVALUE may provide correction if the transmit power reference level ofthe receiving station is transmitted, instead of the actual transmitpower.

α is a weighting value which is a measure of the quality of theestimated path loss and is, preferably, based on the number of timeslots between the time slot of the last path loss estimate and the firsttime slot of the communication transmitted by the transmitting station.The value of α is between zero and one. Generally, if the timedifference between the time slots is small, the recent path lossestimate will be fairly accurate and α is set at a value close to one.By contrast, if the time difference is large, the path loss estimate maynot be accurate and the long term average path loss measurement is mostlikely a better estimate for the path loss. Accordingly, α is set at avalue closer to one. Equations 3 and 4 are equations for determining α.

α=1−(D−1)/(D _(max)−1)  Equation 3

α=max {1−(D−1)/(D _(max-allowed)−1),0}  Equation 4

where the value, D, is the number of time slots between the time slot ofthe last path loss estimate and the first time slot of the transmittedcommunication which will be referred to as the time slot delay. If thedelay is one time slot, α is one. D_(max) is the maximum possible delay.A typical value for a frame having fifteen time slots is seven. If thedelay is D_(max), α is zero D_(max-allowed) is the maximum allowed timeslot delay for using open loop power control. If the delay exceedsD_(max-allowed), open loop power control is effectively turned off bysetting α=0.

As the data rates N(t) and M(t) change from time-to-time, the inventivesystem of FIG. 7 compensates for the change in required power, asopposed to waiting for a revised target SIR to be determined by theouter loop to compensate for the data rate change. Thus, for open looppower control, the invention virtually eliminates the period of timewhen the transmitted signal is sent with excess power due to a data ratechange.

With respect to the closed loop system of FIG. 4 with N(t) equal to M(t)in the steady state, ignoring the variance of a fading channel or anyvariable interference, the target SIR will settle at a quiescent pointyielding the desired data quality. This is the equivalent of the singlerate system of FIG. 2. With variable multirate, however, at some time t,N and/or M changes. As described above, where this results in animprovement to the measured data quality metric, more energy than isactually required is transmitted. However, the measured SIR does notchange with changes in N and M, because the SIR is measured before thedown-conversion with it concomitant increase in Eb/No (or SIR) perrepeated bit. Since the outer loop operates at a relatively low rate, inthe short term, the power control commands sent back to the transmitterwill no longer be accurate. However, eventually the outer loop willdetect the improved signal quality and compute a lower target SIR forthe inner loop to compensate for what it perceives as too-high signalquality. When that happens, this too-low target SIR will downward biasthe step up/down decisions and thus reduce transmitter power. This inturn will result in below-required signal quality at the receiver.Eventually, the outer loop will respond to the degraded signal qualitywith a higher target SIR, and in the steady state the system willeventually converge to the correct power level. Until then, the receivedsignal will be degraded.

FIG. 8 illustrates the invention as it applies to a closed loop powercontrol system for variable multirate data where corresponding elementshave the same reference numerals as in FIG. 4. In the transmitter 51 ofthe transmitting station 50, the converter 67 provides an additionalinput 69 to the scale factor generating processor 55. The converterprovides a signal equivalent to √{square root over ( )}(N(t)/M(t)) sothat the scale factor output by the processor 55 via output 53 is afunction of N(t)/M(t) as described above in connection with the openloop system of FIG. 7.

In the receiver 70, the converter 87 outputs a signal equivalent toN(t)/M(t) to a combiner 88, preferably a multiplier. The output of thetarget SIR processor 74 is diverted to the combiner 88. The combiner 88combines the rate change data from the converter 87 and the target SIRdata from the processor 74 and outputs an adjusted target SIR to thecombiner 76.

Through this configuration, the processor 74 effectively outputs anominal target SIR. By applying the factor N(t)/M(t) to the nominaltarget SIR determined from the measured signal quality, a more rapidresponse is made to compensate or adjust for a change received power dueto a data rate change.

As data rates N(t) and M(t) change from time-to-time, the system of FIG.8 rapidly compensates for the change in required power in thetransmitter and the changed expected received signal strength in thereceiver, as opposed to waiting for the outer loop to compensate for thedata rate change. Thus, for closed loop power control system of FIG. 8the period of time when the received signal is received below acceptablequality due to a data rate change is reduced.

Although various components have been identified separately within therespective transmitting and receiving stations, those of ordinary skillin the art will recognize that various elements can be combined. Forexample, combiner 88 of the system of FIG. 8 can be embodied in a singleprocessor with processor 74. Other variations and modificationsconsistent with the invention will be recognized by those of ordinaryskill in the art.

What is claimed is:
 1. A method of controlling transmitter power in awireless communication system in which user data is processed as amultirate signal having a rate N(t) where N(t) is a function of time, inwhich the user data signal having rate N(t) is converted into atransmission data signal having a faster rate M(t) for transmission andin which transmitter power is controlled by a closed loop system wherethe transmission power is adjusted by applying a scale factor inresponse to step up/down data generated by a receiver of the transmitteddata, the step up/down data being based in part on relatively slowlycollected quality of data received by comprising: determining stepup/down data as a function of N(t)/M(t) such that a change in the userdata signal rate or the data rate of the transmission data signal iscompensated for in advance of a quality of data based adjustmentassociated with such a data rate change.
 2. The method of claim 1wherein the user data signal having rate N(t) is converted into thetransmission data signal having a faster rate M(t) by repeating selecteddata bits whereby the energy per bit to noise spectrum density ratio isincreased in the transmission data signal.
 3. The method of claim 1wherein the step up/down data is generated by the receiver by combiningmeasured interference power data of the signal received from thetransmitter with target signal to interference ratio (SIR) data which iscomputed by multiplying nominal target SIR data, based on relativelyslowly collected received signal quality data, by a factor N(t)/M(t) sothat the target SIR data is quickly adjusted when a change in data rateoccurs.
 4. The method of claim 3 wherein the user data signal havingrate N(t) is converted into the transmission data signal having a fasterrate M(t) by repeating selected data bits whereby the energy per bit tonoise spectrum density ratio is increased in the transmission datasignal.
 5. The method of claim 3 wherein the transmitter computes thescale factor based on the received step up/down data and √{square rootover ( )}(N(t)/M(t)).
 6. The method of claim 1 wherein the transmittercomputes the scale factor as a function of the received step up/downdata and N(t)/M(t).
 7. The method of claim 6 wherein the user datasignal having rate N(t) is converted into the transmission data signalhaving a faster rate M(t) by repeating selected data bits whereby theenergy per bit to noise spectrum density ratio is increased in thetransmission data signal.
 8. The method of claim 7 wherein thetransmitter computes the scale factor based on the received step up/downdata and √{square root over ( )}(N(t)/M(t)).
 9. A closed looptransmission power control system for a wireless communication system inwhich user data is processed as a multirate signal having a rate N(t)where N(t) is a function time, in which the user data signal having rateN(t) is converted into a transmission data signal having a faster rateM(t) for transmission and in which the transmission power is adjusted byapplying a scale factor in response to step up/down data, comprising: areceiver which receives the M(t) rate transmission data signal andgenerates the step up/down data including: a data signal rate converterwhich decreases the data rate of received transmission data M(t) toproduce a user data signal having a lower data rate N(t); a data qualitymeasuring device for measuring the quality of data of the user datasignal; circuitry for computing step up/down data based in part on themeasured quality of data of the user data signal; and said data signalrate converter associated with said circuitry to provide rate data suchthat said circuitry computes step up/down data as a function ofN(t)/M(t) such that a change in the user data signal rate or the rate ofthe transmission data signal is compensated for in advance of a qualityof data based adjustment associated with such data rate change.
 10. Theclosed loop system of claim 9 further comprising a transmitter having adata signal rate convertor which converts the user data signal havingrate N(t) into the transmission data signal having a faster rate M(t) byrepeating selected data bits whereby the energy per bit to noisespectrum density ratio is increased in the transmission data signal. 11.The closed loop system of claim 9 wherein the receiver furthercomprises: an interference measuring device for measuring the power ofan interference signal received with the M(t) rate transmission datasignal; said data quality measuring device outputting a nominal targetSIR data based on relatively slowly collected received data qualitydata; and said circuitry computing the step up/down data by combiningmeasured interference power data of the signal received from thetransmitter with target signal to interference ratio SIR data which iscomputed by multiplying the nominal target SIR data by a factorN(t)/M(t) so that the target SIR data is quickly adjusted when a changein data rate occurs.
 12. The closed loop system of claim 11 furthercomprising a transmitter having a data signal rate convertor whichconverts the user data signal having rate N(t) into the transmissiondata signal having a faster rate M(t) byrepeating selected data bitswhereby the energy per bit to noise spectrum density ratio is increasedin the transmission data signal.
 13. The closed loop system of claim 12wherein the transmitter includes a processor which computes the scalefactor based on the step up/down data and √{square root over ()}(N(t)/M(t)).
 14. The closed loop system of claim 9 further comprisinga transmitter having a processor which computes the scale factor as afunction of the step up/down data and N(t)/M(t).
 15. The closed loopsystem of claim 14 further comprising a transmitter having a data signalrate convertor which converts the user data signal having rate N(t) intothe transmission data signal having a faster rate M(t) by repeatingselected data bits whereby the energy per bit to noise spectrum densityratio is increased in the transmission data signal.
 16. The method ofclaim 14 wherein the transmitter processor computes the scale factorbased on the step up/down data and √{square root over ( )}(N(t)/M(t)).